This invention relates to a device for dispensing medicaments.
Conventional administration of drugs takes two general forms--periodic injection or ingestion, or continuous infusion. Periodic administration has the disadvantage that the drug level within the body varies from above optimum initially and falls below optimum, resulting in poor maintenance of the patient and inefficient use of the drug. Increasing the number of applications minimizes the adverse effects of high dosages and improves efficiency but results in higher costs and more inconvenience to the patient. Infusion therapy can provide a relatively constant dose level but is limited by the bulky nature of the medicament preparation and by the expert care needed for safe administration.
In recent years, polymeric membranes have been used to encapsulate medicament preparations to slow and control the release of the active substance, allowing the body to be maintained at the optimum level over a relatively long time. Controlled release formulations have two deficiencies which limit their use--the amount of drug that can be encapsulated and implanted is relatively small, and it is not possible to vary the rate of release of the drug. The inability to vary the release rate limits the use to those agents which have a constant demand rate or a constant clearance rate, and is not entirely satisfactory for insulin therapy.
Insulin is required by the body in varying amounts with a greater amount being required during and immediately after a meal when the glucose level rises. The controlled release formulation while maintaining a basal amount of insulin in the blood, cannot increase the amount of insulin to counteract the increased glucose level after a meal.
It has been proposed, for example, in U.S. Pat. No. 3,923,060 to E. H. Ellinwood, Jr., to provide an implantable apparatus for dispensing medications within the body over a long period of time in accordance with the needs of the patient by providing sensors which monitor a particular body condition and powered dispensing means responsive to the sensed data. The aforesaid patent also describes a device specifically for dispensing insulin, having two dispensing elements, one to dispense a daily average dose on a regular basis and one to dispense intermittently when the need arises. The device described requires that each dispensing element is provided with a separate pump, pump driving means and associated logic circuit. This arrangement requires two separate dispensing units and associated energizing means, and in the event of an interruption of energy, no medication would be dispensed.